Linear actuator



March 29, 1966 J, BRANDSTADTER 3,242,820

LINEAR ACTUATOR Original Filed March 27. 1961 IN VEN TOR. JZcK/M EMA057412752 United States Patent Office 3,242,820 Patented Mar. 29, 1,966.

3,242,820 LINEAR ACTUATOR Jack M. Brandstadter, Royal Oak, Mich.,assignor to Cadillac Gage Company, Roseville, Mich. Originalapplication. Mar. 27, 1961, Ser. No. 98,549, now Patent No. 3,141,388,dated. July 21, 1964. Divided and this. application Dec. 13, 1963, Ser.No. 347,638 3 Claims. (Cl. 91-167) This is a division of applicationSerial No- 98,549, now Patent No. 3,141,388, issued July 21, 1964.

This. invention relates to improvements in linear actuators, andmore.particularly relates to servo-mechanisms for linearly; positioning ashaft by fluid means in re.- sponse to sel'ectivei'nput signals.

In the art of data processing, digital computers, machine-tools,automation, and the like, there exists a need for deviceswhichaccurately position a shaft or a movabl'e reference output element inresponse to information applied to the input of the device. Variousservo-mechanismsof'this nature have been proposed; they may be actuatedby, electrical means or by purely mechanical means- Itflis an object ofthis invention to provide a linear shaft actuator and positioner whichis selectively operated by fluid pressure means. The fluid may be oil,Water, compressed air, a gas, steam, or any other like fluid.

The transmission of control information in systems of the characterherein. mentioned is commonly carried out in. the binary numericalsystem- It is frequently desirable to convert the digital representationof. the binary numher into an analogue equivalent such as the. linearposition, of' a movable. reference output element or an angular shaftrotation. It is, therefore, another object of this invention to provideselectively operable fluid motor means for converting a binaryinformation into. an analogue equivalent in the form of a. linear shaftpositi'on. It is. apparent. to those skilled in the art that such ananalogue. linear. displacement and. positioning can. be easilyconverted, in applications where so desired, into anv angular. shaftrotation and positioning through a simple, rocker. arm. assembly, rackandv pinion assembly, or thelike.

It is a further object of this invention to provide a compact,self-contained, fluid motor powered binary to linear shaftposition.converter..

It is another object of. this invention to provide a linear actuatorutilizing a relatively small number of simpleelementary identicalpartsin order to reduce manufacturing cost. and inventory- It is anadditional object of this invention to provide a. linear actuatordeveloping a great power with practically no lag in operation and almostinstantaneous response.

It is a further object of this invention to provide a linear actuatorhaving a. number of discrete positions which correspond to. the formulaN=2 in which N denotes. the number of discrete positions and n denotesthe. number of individual unit elements being placed in series within acommon housing. For example, if it is desired to. provide for 8differentdiscrete positions of the output reference element, the numberof unit elements orstages to be used is 3; ifv 128 discrete positionsare required,.7 unit. elements, or stages, must be placed within the,housing.

A further object, of this invention is to have a predetermined. numberof discrete positions which are accurately repeatable ad infinitum,together with positive indexing at each discrete position.

Still. a further object of this invention is to provide a linearactuator which has a response time that can be tailored according to therequirements of the controlled equipment and which has positivedampening of the acceleration and deceleration of the movable shaft.

An additional object of this invention is to provide a device which canutilize readily available pressure fluid hardware, tubings, valves,accumulators, and the like.

Another object is to provide a functional unit, endowed with high.reliability and long life.

Additional objects and advantagesof the invention will become apparentfrom the following description and appended. claims, taken in connectionwith the accompanying drawings, which disclose, by way of example, theprinciples of this invention and some of the best modes which have beencontemplated of applying these principles.

In the drawings:

FIG. 1 is a longitudinal cross-section view ofv an embodimentv of theinvention with some parts broken away to show their internalconfiguration;

FIG. 2 is a transversal cross-section view takenalong line 88 of FIG. 1;

FIG. 3 is a top view of one of the component parts shown in FIG. 1;

FIG. 4 is a side elevation view of the part. shown. in FIG. 3;

FIG. 5 is an end view from line 1111-. of FIG. 4..

The embodiment of a linear actuator or positioner according to theprinciple of the invention is illustrated in FIGS. 1-5 as having sevenstages, each stage: consisting of only one slidable member disposedwithin the main bore of a housing. When actuatedv by fluid pressure,each stage member is adapted to travela predetermined distance definedbetween abutments, displacing at the same time all the stages between itand the; cute put shaft, and. a combination of stages displaces theoutput shaft the sum of the strokes of the stages being actuated. Thedevicev is loaded toward its retracted position by supply fluid pressureacting upon a partial area of. the seventh stage, in a directionopposite to the direction in which the individual stages travel, when.actuated.

In the drawings of FIGS. 1 and 2, a housing 400 having a cylindricalmain bore 402 is. closed on one end by an end cap 404, fastened thereonby means of the cap screws. or bolts 406. The end cap has, ashoulder-like integralv portion 408 fitted into the housing bore andprovided with a groove 410 and. an O-seal ring 412. An integrally formedlink 414 projectsa certain distance into the bore and has an upturnedend portion or flange 416-. Within the main bore 402 is disposed aseries of piston elements designed generally by numerals 420,, 422, 424,426, 428, 430 and 432, having a lap fit, with the, bore and beingslidable therein.

FIGS. 3-5 show in detail one such piston element. A piston body 434 hasan outside diameter adapted to slid,- ably fit Within the housing mainbore. The bodyhas two integrally formed L-shaped. projecting extensions:a pushrod 436 and a connecting link 438. Push rod 436 has a downturnedend portion or flange. 440 having an outer end face 442 adapted to abutagainst the side face 444 of the preceding piston, and an inner face orabutment surface 446. Connecting link 438 has an upturned end portion orflange 447 with an inner face or abutment surface 448. A longitudinalnotch or groove 450 in the stem or push rod 436 gives the requiredclearance for the flange 447 of the preceding piston connecting link. Alongitudinal notch or groove 453 in the stem of the connecting link 438gives, in a similar fashion, the required clearance for the flange 440of the following piston push rod.

Such an arrangement prevents each piston element from rotatingrelatively to the piston elements adjacent thereto, and from tilting soas to become wedged in the bore.

FIG. 1 shows how the piston elements are interlinked within the mainbore 402. The first piston element 420 has its push rod 436 interlinkedwith the projecting ele- I 'ment 414 integral with the end cap 404. Thesecond piston element 422, and all the subsequent piston elements havethe end faces 442 of their respective push rods 436 in contact with theside 444 of the preceding piston when the device is in a retractedposition as shown in FIG. 1. The last piston, 432, has a reduceddiameter rod-like portion 450 adapted to receive the output shaft 452adjustably fastened in a threaded bore 451 disposed substantially alongthe axis of rod-like portion 450. An end cap 454 is fastened upon thehousing by the cap screws or bolts 456. The end cap has a groove with anO-ring seal 458 to prevent leakage to the outside of the housing, and abore 460 with a groove and an O-ring seal 462 to allow the rod-likeportion 450 to slide in and out from the housing. The annular chamber464, thus disposed between the end face 466 of the piston 432 and theinner face of the end cap 454, is filled with pressure supply fluidadmitted through passageway 468 from manifold 470. The fluid exerting apressure upon the face 466 of piston 432 furnishes the biasing forcenecessary to retract the device in the same manner as hereinbeforeexplained in connection with the preceding embodiments ofthe invention.

Control valves 472, 474, 476, 478, 480, 482 and 484 are disposed on thehousing 400 to control the stages of the actuator by admitting orexhausting pressure supply fluid through the passageways 473, 475, 477,479, 481, 483 and 485. Fluid is thus'admitted, as required, in thecorresponding chambers 492, 494, 496, 498, 500, 502 and 504 wherepressure is exerted on the opposing faces of two consecutive pistonsforming the end walls of the respective chambers. For example, if fluidis admitted into chamber 498, when the device is in a retractedposition, pressure will be exerted upon face 444 of piston 424 and uponface 445 of piston 426. Piston 424 cannot move because the end face ofits push rod 436 abuts against the adjacent face of the preceding piston422. Piston 422 cannot move for the same reason, i.e., because its pushrod abuts against the adjacent face of the next preceding piston 420which, in turn, is prevented to move by its own push rod abuttingagainst the face of the end plate shouldered portion 408. However, thefluid pressure in chamber 498 acting upon the face 445 of piston 426pushes piston 426 until the abutment 446 contacting the abutment 448prevents further travel. Piston 426 has thus travelled a distance dwhichis equal to the distance separating the two abutments 446 and 448when the device was at rest. The travel or stroke of piston 426 istransmitted to the next following piston through the push rod 436integral with the next following piston 428. In the same manner, thelinear displacement of piston 428 is transmitted to piston 430 and topiston 432, the latter displacing the output shaft 452 of the samequantity d. If fluid is now admitted to chamber 500, piston 428 travelsa distance e which is its stroke as determined by the distanceseparating its own abutment 446 from the abutment 448 of the nextpreceding piston. As piston 428 had already travelled a distance d, itstotal travel is now d+e. This travel is transferred to piston 430 andfrom it to piston 432 and the output shaft 452. in the mannerhereinbefore explained. Although the sequence has been arbitrarilychosen in such a way as to describe the events as taking'place insucceeding order, for the sake of simplicity-of explanation, operationof the different stages of the actuator may take place in any order orcontemporaneously.

In this embodiment of the invention, the stroke of the first stage,piston 420, is arbitrarily chosen to be a quantity a. The stroke of thesecond Stage, piston 422, is

4 arbitrarily chosen to be a value b twice thatof a, and so on to thelast stage, piston 432, which has a proper stroke g which is twice thatof the preceding stage 9. Therefore, with seven stages as illustrated,128 discrete positions are available including the fully retractedposition 0 (binary 0000000) and the fully extended position (binary1111111).

In the embodiment of the invention as shown, fluid pressure means actingupon an area of the last stage bias the actuator toward its retractedposition. Other means, such as a coil spring, could be used as a biasingmeans without detracting from the scope and spirit of the invention.

A calibrated orifice to regulate the flow of biasing pressure fluid suchas shown and described in connection with the embodiment of theinvention forming the subject matter of co-pending application SerialNo. 347,- 637 can also be used in combination with the presentembodiment of the invention, if so desired. Also any number of stagesmay be used in the device instead of the seven stages as herein shown.For instance, an actuator comprising eight stages would give 256possible discrete positions of the output shaft and an actuator-havingonly five stages would give 32 possible discrete positions.

The device has been shown with a stationary-housing and a movable shaft.However, the output shaft could be maintained stationary and the housingcould be allowed to move without departing from the scope and spirit ofthe invention.

Although the illustrated embodiment has been shown with the mostsignificant digit stage connected tov the output shaft while the leastsignificant digitstage was connected to the stationary reference, it isobvious that this arrangement could be reversed, or if so preferred, anyorder of digit stages could be used. It is also obvious that the devicecould be non-binary, and the ratio between stage strokes could be chosenas best fitting the purpose intended for the apparatus.

It is. obvious that, for some special applications, several of suchactuators as herein described and illustrated could be placed in series,in opposition or in parallel. For example, the output shaft of oneactuator could be connected to the housing of another actuator in orderto give a maximum resultant stroke which is the sum of the maximumstrokes of each individual actuator. Two housings could be placed backto back or two actuators could be placed in a common housing with twooutput shafts movable through both ends of the housing.

The above example is given only for illustrative pur.- pose of a few of.the possible combinations contemplated and it will be apparent to thoseskilled in the art that there is a great number of such possiblecombinations.

It is obvious that various changes, additionsand omissions of elementsmay be made in details within the scope and spirit of the invention; andit is, therefore, to be understood that the invention is not to belimited to the specific details, examples, and embodiment shown anddescribed.

What is claimed is:

1. In a positioner for linearly positioning a movable reference elementin relation to a stationary reference element, wherein said positionercomprises a stationary elongated housing defining the stationaryreference element having a substantially cylindrical bore with an endclosed by a first end plate and another end provided with a second endplate having a substantially centrally disposed opening, a slidableoutput shaft defining the movable reference element longitudinallymovable through the opening in said second end plate, a plurality ofcascaded motor stages slidably disposed end-to-end within the bore insaid housing intermediate the closed endof said bore and the outputshaft, a source of pressurized fluid, and valving and conduit means forselectively connecting and disconnecting the motor stages to and fro thesource of pressurized fluid,

the improvement characterized by each one of said motor stagescomprising:

a piston member having a body portion adapted to slidably fit within thebore in the housing and having a first and a second L-shaped extensionsprojecting from the opposite faces of said body portion,

the first of said L-shaped extensions defining a pushrod element and thesecond of said L-shaped extensions defining a connecting link element,both said push-rod and connecting link elements being provided with astem having an end flange portion disposed substantially at right angleto the axis of the piston member and having an inner end face and anouter end face,

said end flange portion of the push-rod element being adapted totransversely project into a corresponding groove-like recess in the stemof the connecting link element associated with the next preceding pistonmember for preventing consecutive piston members from rotating andtilting relatively to each other,

the inner end face of said end flange portion of the push-rod elementbeing normally a predetermined distance away from the inner end face ofthe end flange portion of the connecting rod element interlinkedtherewith,

the outer end face of said flange portion of the pushrod element beingnormally adapted to abut against the end face of the body portion of thepiston mem ber immediately preceding,

said end flange portion of the connecting link element being adapted toproject into a corresponding groovelike recess in the stem of thepush-rod element associated with the next consecutive piston member forpreventing consecutive piston members from rotating and tiltingrelatively to each other,

the inner end face of said end flange portion of the connecting linkelement defining an abutment being normally said predetermined distanceaway from the inner end face of the end flange portion of the pushrodelement and adapted to engage therewith for limiting the permissibletravel of two consecutive piston members relatively to each other,

the outer end face of said end flange portion of the connecting linkelement being normally a small distance away from the end face of thepiston body portion of the next consecutive piston member,

the stems of said push-rod element and of said connecting link elementbeing symmetrically arranged relatively to the longitudinal axis of thepiston member associated therewith and being disposed on alternate sidesof an imaginary plane situated in said axis with the respective endflange portions thereof substantially at right angle to said axis andprojecting centripetally relatively the bore in said housing,

a connecting link element projecting from the inner side of the endplate closing the closed end of the bore in the housing which is adaptedto cooperate with the push-rod element of the first one of said pistonmembers,

the last one of said piston members being devoid of connecting linkelement and being attached directly to the output shaft,

the body portions or" each pair of two consecutive piston membersdefining a substantially annular chamber disposed in the bore of saidhousing between such two body portions of consecutive piston members,

port means in the bore of the housing for admitting pressurized fluidinto each said annular chamber for causing displacement of the pistonmember situated towards the output shaft, thus displacing at the sametime all the piston members between said piston member and the outputshaft by means of the end face of the body portion of each of saidpiston members engaging the outer end face of the pushrod element ofeach consecutive piston member, the maximum travel of each piston memberrelatively to the piston member immediately preceding being limited bystop means defined by the inner end face of the end flange portion ofeach push-rod element and the inner end face of the end flange portionof each connecting link element, and

biasing means exerted upon the last piston member in a direction thattends to maintain the outer end face of the end flange portion of thepush-rod element of each piston member in contact with the correspondingend face of the next preceding piston body portion, and the outer endface of the end flange portion of the push-rod element of the firstpiston member in contact with the inner side of the end plate therebybiasing the actuator to its retracted condition.

2. The improvement as claimed in claim 1 wherein the biasing means isthe pressurized fluid acting upon a shoulder area of the last pistonmember, said area being the end face of the body portion of said lastpiston member situated toward the output shaft and being substantiallysmaller than the effective area upon which said pressurized fluid exertsa force that causes the individual piston members to be displaced.

3. The improvement as claimed in claim 1 wherein the predetermineddistance between the inner end face of the end flange portion of theconnecting link elements and the inner end face of the end flangeportion of the pushrod elements varies from stage to stage according toa binary series.

References Cited by the Examiner UNITED STATES PATENTS 2,443,642 6/1948Rockwell 6054.5 2,699,757 1/1955 Tornkvist 9l167 2,969,042 1/1961 Litz91-167 2,974,492 3/ 1961 Gilovich 91-167 OTHER REFERENCES IBM TechnicalDisclosure Bulletin (vol. 1, No. 4, December 1958, pp. 22, 91-357).

SAMUEL LEVINE, Primary Examiner.

FRED E. ENGELTHALER, Examiner.

P. T. COBRIN, Assistant Examiner.

1. IN A POSTIONER FOR LINEARLY POSITIONING A MOVABLE REFERENCE ELEMENT IN RELATION TO A STATIONARY REFERENCE ELEMENT, WHEREIN SAID POSITIONER COMPRISES A STATIONARY ELONGATED HOUSING DEFINING THE STATIONARY REFERENCE ELEMENT HAVING A SUBSTANTIALLY CYLINDRICAL BORE WITH AN END CLOSED BY A FIRST END PLATE AND ANOTHER END PROVIDED WITH A SECOND END PLATE HAVING A SUBSTANTIALLY CENTRALLY DISPOSED OPENING, A SLIDABLE OUTPUT SHAFT DEFINING THE MOVABLE REFERENCE ELEMENT LONGITUDINALLY MOVABLE THROUGH THE OPENING IN SAID SECOND END PLATE, A PLURALITY OF CASCADED MOTOR STAGES SLIDABLY DISPOSED END-TO-END WITHIN THE BORE IN SAID HOUSING INTERMEDIATE THE CLOSED END OF SAID BORE AND THE OUTPUT SHAFT, A SOURCE OF PRESSURIZED FLUID, AND VALVING AND CONDUIT MEANS FOR SELECTIVELY CONNECTING AND DISCONNECTING THE MOTOR STAGES TO AND FROM THE SOURCE OF PRESSURIZED FLUID, THE IMPROVEMENT CHARACTERIZED BY EACH ONE OF SAID MOTOR STAGES COMPRISING: A PISTON MEMBER HAVING A BODY PORTION ADAPTED TO SLIDABLY FIT WITHIN THE BORE IN THE HOUSING AND HAVING A FIRST AND SECOND L-SHAPED EXTENSIONS PROJECTING FROM THE OPPOSITE FACES OF SAID BODY PORTION, THE FIRST OF SAID L-SHAPED EXTENSIONS DEFINING A PUSHROD ELEMENT AND THE SECOND OF SAID L-SHAPED EXTENSIONS DEFINING A CONNECTING LINK ELEMENT, BOTH SAID PUSH-ROD AND CONNECTING LINK ELEMENTS BEING PROVIDED WITH A STEM HAVING AN END FLANGE PORTION DISPOSED SUBSTANTIALLY AT RIGHT ANGLE TO THE AXIS OF THE PISTON MEMBER AND HAVING AN INNER END FACE AND AN OUTER END FACE, SAID END FLANGE PORTION OF THE PUSH-ROD ELEMENT BEING ADAPTED TO TRANSVERSELY PROJECT INTO A CORRESPONDING GROOVE-LIKE RECESS IN THE STEM OF THE CONNECTING LINK ELEMENT ASSOCIATED WITH THE NEXT PRECEDING PISTON MEMBER FOR PREVENTING CONSECUTIVE PISTON MEMBERS FROM ROTATING AND TILTING RELATIVELY TO EACH OTHER, THE INNER END FACE OF SAID END FLANGE PORTION OF THE PUSH-ROD ELEMENT BEING NORMALLY A PREDETERMINED DISTANCE AWAY FROM THE INNER END FACE OF THE END FLANGE PORTION OF THE CONNECTING ROD ELEMENT INTERLINKED THEREWITH, THE OUTER END FACE OF SAID FLANGE PORTION OF THE PUSHROD ELEMENT BEING NORMALLY ADAPTED TO ABUT AGAINST THE END FACE OF THE BODY PORTION OF THE PISTON MEMBER IMMEDIATELY PRECEDING, SAID END FLANGE PORTION OF THE CONNECTING LINK ELEMENT BEING ADAPTED TO PROJECT INTO A CORRESPONDING GROOVELIKE RECESS IN THE STEM OF THE PUSH-ROD ELEMENT ASSOCIATED WITH THE NEXT CONSECUTIVE PISTON MEMBERS FOR PREVENTING CONSECUTIVE PISTON MEMBERS FROM ROTATING AND TILTING RELATIVELY TO EACH OTHER, THE INNER END FACE OF SAID END FLANGE PORTION OF THE CONNECTING LINK ELEMENT DEFINING AN ABUTMENT BEING NORMALLY SAID PREDETERMINED DISTANCE AWAY FROM THE INNER END FACE OF THE END FLANGE PORTION OF THE PUSHROD ELEMENT AND ADAPTED TO ENGAGE THEREWITH FOR LIMITING THE PERMISSIBLE TRAVEL OF TWO CONSECUTIVE PISTON MEMBERS RELATIVELY TO EACH OTHER, THE OUTER END FACE OF SAID END FLANGE PORTION OF THE CONNECTING LINK ELEMENT BEING NORMALLY A SMALL DISTANCE AWAY FROM THE END FACE OF THE PISTON BODY PORTION OF THE NEXT CONSECUTIVE PISTON MEMBER, THE STEMS OF SAID PUSH-ROD ELEMENT AND OF SAID CONNECTING LINK ELEMENT BEING SYMMETRICALLY ARRANGED RELATIVELY TO THE LONGITUDINAL AXIS OF THE PISTON MEMBER ASSOCIATED THEREWITH AND BEING DISPOSED ON ALTERNATE SIDES OF AN IMAGINARY PLANE SITUATED IN SAID AXIS WITH THE RESPECTIVE END FLANGE PORTIONS THEREOF SUBSTANTIALLY AT RIGHT ANGLE TO SAID AXIS AND PROJECTING CENTRIPETALLY RELATIVELY THE BORE IN SAID HOUSING, A CONNECTING LINK ELEMENT PROJECTING FROM THE INNER SIDE OF THE END PLATE CLOSING THE CLOSED END OF THE BORE IN THE HOUSING WHICH IS ADAPTED TO COOPERATE WITH THE PUSH-ROD ELEMENT OF THE FIRST ONE OF SAID PISTON MEMBERS, THE LAST ONE OF SAID PISTON MEMBERS BEING DEVOID OF CONNECTING LINK ELEMENT AND BEING ATTACHED DIRECTLY TO THE OUTPUT SHAFT, THE BODY PORTIONS OF EACH OF TWO CONSECUTIVE PISTON MEMBERS DEFINING A SUBSTANTIALLY ANNULAR CHAMBER DISPOSED IN THE BORE OF SAID HOUSING BETWEEN SUCH TWO BODY PORTIONS OF CONSECUTIVE PISTON MEMBERS, PORT MEANS IN THE BORE OF THE HOUSING FOR ADMITTING PRESSURIZED FLUID INTO EACH SAID ANNULAR CHAMBER FOR CAUSING DISPLACEMENT OF THE PISTON MEMBER SITUATED TOWARDS THE OUTPUT SHAFT, THUS DISPLACING AT THE SAME TIME ALL THE PISTON MEMBERS BETWEEN SAID PISTON MEMBERS AND THE OUTPUT SHAFT BY MEANS OF THE END FACE OF THE BODY PORTION OF EACH OF SAID PISTON MEMBERS ENGAGING THE OUTER END FACE OF THE PUSHROD ELEMENT OF EACH CONSECUTIVE PISTON MEMBER, THE MAXIMUM TRAVEL OF EACH PISTON MEMBER RELATIVELY TO THE PISTON MEMBER IMMEDIATELY PRECEDING BEING LIMITED BY STOP MEANS DEFINED BY THE INNER END FACE OF THE END FLANGE PORTION OF EACH PUSH-ROD ELEMENT AND THE INNER END FACE OF THE END FLANGE PORTION OF EACH CONNECTING LINK ELEMENT, AND BIASING MEANS EXERTED UPON THE LAST PISTON MEMBER IN A DIRECTION THAT TENDS TO MAINTAIN THE OUTER END FACE OF THE FLANGE PORTION OF THE PUSH-ROD ELEMENT OF EACH PISTON MEMBER IN CONTACT WITH THE CORRESPONDING END FACE OF THE NEXT PRECEDING PISTON BODY PORTION, AND THE OUTER END FACE OF THE END FLANGE PORTION OF THE PUSH-ROD ELEMENT OF THE FIRST PISTON MEMBER IN CONTACT WITH THE INNER SIDE OF THE END PLATE THEREBY BIASING THE ACTUATOR TO ITS RETRACTED CONDITION. 